Magnetic disk device and method for setting recording area

ABSTRACT

According to one embodiment, a magnetic disk device including a disk, a head, and a controller which sets a first track pitch based on fringing when a second track is written, sets a second track pitch based on fringing when a third track is written, calculates a difference between the first track pitch and the second track pitch, sets, when the difference is less than or equal to a reference value, an area to which the first track is written in a first recording area, and sets, when the difference is greater than the reference value, the area to which the first track is written in a second recording area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/911,545filed on Mar. 5, 2018 and based upon and claims the benefit of priorityfrom Japanese Patent Application No. 2017-167156, filed Aug. 31, 2017,the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic disk deviceand a method for setting a recording area.

BACKGROUND

In recent years, various technologies have been developed to increasestorage capacity in magnetic disk devices. In one of the technologies,magnetic disk devices use shingled magnetic recording (SMR) to writedata. The shingled magnetic recording is a recording system for writingdata such that the current track partially overlaps the previouslywritten adjacent track (hereinafter, simply referred to as the adjacenttrack). When magnetic disk devices write data by shingled magneticrecording, the track density (tracks per inch: TPI) of disks can beimproved in comparison with normal recording (normal magneticrecording).

Magnetic disk devices used for shingled magnetic recording set arecording area for writing data by shingled magnetic recording and arecording area for writing data by normal recording. When data iswritten, magnetic disk devices may have the effect of fringing on theadjacent tracks. In shingled magnetic recording, the direction in whichdata is written is determined. Thus, the effect of fringing from onlyone of the two tracks adjacent to the target track should be taken intoconsideration. Therefore, the track pitch between the target track andthe adjacent track can be narrow. In normal recording, in considerationof the effect of fringing from the two tracks adjacent to the targettrack, it is necessary to set the track pitch between the target trackand the two adjacent tracks so as to be great.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a magnetic diskdevice according to an embodiment.

FIG. 2 is a pattern diagram showing an example of the position of a headfor a disk according to the embodiment.

FIG. 3 is a pattern diagram showing an example of the fringing width forthe position of the head on the disk according to the embodiment.

FIG. 4 is a pattern diagram shown for explaining an example of a methodfor setting a track pitch according to the embodiment.

FIG. 5 shows an example of the table of a normal recording areaaccording to the embodiment.

FIG. 6 shows an example of the table of the normal recording areaaccording to the embodiment.

FIG. 7 shows an example of the table of the normal recording areaaccording to the embodiment.

FIG. 8 shows an example of the table of the normal recording areaaccording to the embodiment.

FIG. 9 shows an example of the table of the normal recording areaaccording to the embodiment.

FIG. 10 shows an example of the table of the normal recording areaaccording to the embodiment.

FIG. 11 shows an example of the table of the normal recording areaaccording to the embodiment.

FIG. 12 shows an example of the table of the normal recording areaaccording to the embodiment.

FIG. 13 is a flowchart showing a method for setting the track pitchbetween the target track and an adjacent track according to theembodiment.

FIG. 14 is a flowchart showing a method for setting a normal recordingarea and a shingled magnetic recording area according to the embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetic disk devicecomprises: a disk; a head which writes data to the disk; and acontroller which sets a first track pitch between a first track of thedisk and a second track away from the first track in a first directionof a radial direction of the disk based on fringing when the secondtrack is written, sets a second track pitch between the first track anda third track away from the first track in a second direction oppositeto the first direction based on fringing when the third track iswritten, calculates a difference between the first track pitch and thesecond track pitch, sets, when the difference is less than or equal to areference value, an area to which the first track is written in a firstrecording area for wiring a track to a position away from an adjacenttrack, and sets, when the difference is greater than the referencevalue, the area to which the first track is written in a secondrecording area for writing a track such that the track partiallyoverlaps an adjacent track.

According to another embodiment, a magnetic disk device comprises: adisk; a head which writes data to the disk; a nonvolatile memory; and acontroller which sets, for a plurality of tracks of the disk, a firsttrack pitch set based on fringing when an adjacent track away in a firstdirection of a radial direction of the disk is written, and a secondtrack pitch set based on fringing when an adjacent track away in asecond direction opposite to the first direction is written, records, inthe nonvolatile memory, a first area from an area to which, of thetracks, a first track whose difference between the first track pitch andthe second track pitch is less than or equal to a reference value iswritten to an area to which a second track is written, as a firstrecording area for writing a track to a position away from an adjacenttrack, and records, in the nonvolatile memory, an area of the disk otherthan the first recording area as a second recording area for writing atrack such that the track partially overlaps an adjacent track.

According to another embodiment, a method for setting a recording area,applied to a magnetic disk device comprising a disk and a head whichwrites data to the disk, the method comprises: setting a first trackpitch between a first track of the disk and a second track away from thefirst track in a first direction of a radial direction of the disk basedon fringing when the second track is written; setting a second trackpitch between the first track and a third track away from the firsttrack in a second direction opposite to the first direction based onfringing when the third track is written; calculating a differencebetween the first track pitch and the second track pitch, and when thedifference is less than or equal to a reference value, setting an areato which the first track is written in a first recording area forwriting a track to a position away from an adjacent track; and when thedifference is greater than the reference value, setting the area towhich the first track is written in a second recording area for writinga track such that the track partially overlaps an adjacent track.

An embodiment will be described hereinafter with reference to theaccompanying drawings. The drawings are merely examples, and do notlimit the scope of the invention.

Embodiment

FIG. 1 is a block diagram showing the configuration of a magnetic diskdevice 1 according to an embodiment.

The magnetic disk device 1 comprises a head disk assembly (HDA) asdescribed later, a driver IC 20, a head amplifier integrated circuit(hereinafter, a head amplifier IC or a preamplifier) 30, a volatilememory 70, a buffer memory (buffer) 80, a nonvolatile memory 90, and asystem controller 130 which is a single-chip integrated circuit. Themagnetic disk device 1 is connected to a host system (host) 100.

The HDA comprises a magnetic disk (disk) 10, a spindle motor (SPM) 12,an arm 13 comprising a head 15, and a voice coil motor (VCM) 14. Thedisk 10 is rotated by the spindle motor 12. The arm 13 and the VCM 14constitute an actuator. The actuator drives the VCM 14 such that thehead 15 mounted on the arm 13 moves to the target position on the disk10. Two or more disks 10 and heads 15 may be provided.

In the magnetic disk device 1, as write systems for writing data (ortracks) to the disk 10, shingled magnetic recording (SMR) and normalrecording are applied. The shingled magnetic recording is a recordingsystem for writing a track such that a part of the track overlaps anadjacent track (in other words, a part of the track is written on anadjacent track). In normal recording (normal magnetic recording), atrack is written at a position a particular interval away from theadjacent tracks. In other words, normal recording is a recording systemfor writing a track such that the track does not overlap the adjacenttracks. On a magnetic disk device capable of writing data by shingledmagnetic recording, for example, a device managed (DM) type, a hostaware (HA) type or a host managed (HM) type is mounted as firmware. Onthe magnetic disk device 1 of the present embodiment, HA or HM firmwareis assumed to be mounted. In the HA or HM firmware, the host 100 iscapable of confirming the address or storage capacity of the normalrecording area of the magnetic disk device 1 by a dedicated command.

A data area 10 a available for the user and a system area 10 b to whichinformation necessary for system management is written are allocated tothe recording area of the disk 10. The direction along the circumferenceof the disk 10 is referred to as a circumferential direction. Thedirection perpendicular to the circumferential direction is referred toas a radial direction.

The head 15 comprises a write head 15W and a read head 15R mounted on aslider which is a main body. The write head 15W writes data by applyinga recording magnetic field to the disk 10 and controlling themagnetization direction of the recording layer of the disk 10. The readhead 15R reads the magnetization direction of the recording layer of thedisk 10, in other words, data. The head 15 is inclined at a skew anglewith respect to the circumferential direction of the disk 10 dependingon the position of the disk 10. The skew angle is indicated by the anglebetween the line connecting the rotational center of the actuator andthe central point of the head 15 and a line tangent to a track. When thehead 15 writes data to the disk 10, a recording magnetic field may leakout in the radial direction for a track. The leakage of the recordingmagnetic field of the head 15 or the magnetization transition of thedisk 10 in the radial direction for a track is referred to as fringing.Fringing may have an effect on the surrounding tracks, such asdegradation of data. The distance of fringing in the radial direction(hereinafter, simply referred to as the fringing width) changes inaccordance with the position of the head 15 on the disk 10, in otherwords, the skew angle.

FIG. 2 is a pattern diagram showing an example of the position of thehead 15 for the disk 10 according to the embodiment. In the followingdescription, in the radial direction, the direction to the external sideof the disk 10 is referred to as an external direction (external side),and the opposite direction of the external direction is referred to asan internal direction (internal side).

The data area 10 a is divided into an inner circumferential area IRlocated in the internal direction of the disk 10, an outercircumferential area OR located in the external direction of the disk10, and a middle circumferential area MR located between the innercircumferential area IR and the outer circumferential area OR. The dataarea 10 a includes a shingled magnetic recording area SR for writingdata by shingled magnetic recording, and a normal recording area CR forwriting data by normal recording. The normal recording area CR includesa position ZL in the radial direction at which the skew angle of thehead 15 is zero. In the example shown in FIG. 2, the normal recordingarea CR is located in the middle circumferential area MR. In the exampleshown in FIG. 2, the position ZL is in the middle circumferential areaMR. The normal recording area CR may be located in the innercircumferential area IR or the outer circumferential area OR. In otherwords, the position ZL may be in the inner circumferential area IR orthe outer circumferential area OR. The shingled magnetic recording areaSR is the data area 10 a excluding the normal recording area CR. In theexample shown in FIG. 2, the shingled magnetic recording area SR islocated in the area ranging from the outer circumferential area OR otherthan the normal recording area CR to the middle circumferential area MRand in the area ranging from the inner circumferential area IR to themiddle circumferential area MR.

In FIG. 2, heads 15I, 15M and 15O indicate the head 15 in which the skewangle differs. Head 15I indicates the head 15 inclined at the skew anglelocated in the inner circumferential area IR. Head 15M indicates thehead 15 inclined at the skew angle located in the middle circumferentialarea MR. Head 15O indicates the head 15 inclined at the skew anglelocated in the outer circumferential area OR. In the example shown inFIG. 2, head 15M is located at the position ZL. Thus, heads 15I and 15Oare inclined at a skew angle greater than that of head 15M. In otherwords, in the head 15, the skew angle increases with increasing distancefrom the position ZL at which the skew angle is zero.

FIG. 3 is a pattern diagram showing an example of the fringing width forthe position of the head 15 on the disk 10 according to the presentembodiment. FIG. 3 shows tracks TR1, TR10 and TR100. Track TR1 islocated in the inner circumferential area IR. Track TR10 is located inthe middle circumferential area MR. Track TR100 is located in the outercircumferential area OR. For example, track TR1 is written by head 15Ishown in FIG. 2. For example, track TR10 is written by head 15M shown inFIG. 2. For example, track TR100 is written by head 15O shown in FIG. 2.FIG. 3 shows width W1 of track TR1 in the radial direction (hereinafter,referred to as a track width), track width W10 of track TR10 and trackwidth W100 of track TR100. In FIG. 3, track widths W1, W10 and W100 areequivalent to the width of the write head 15W, and are substantially thesame as each other. FIG. 3 also shows track center TC1 of track TR1,track center TC10 of track TR10 and track center TC100 of track TR100.Track centers TC1, TC10 and TC100 are the tracks of the centralpositions of track widths W1, E10 and W100 at the positions of tracksTR1, TR10 and TR100 in the circumferential direction, respectively. Inother words, track centers TC1, TC10 and TC100 are the tracks of thewrite head 15W. In the example shown in FIG. 3, track centers TC1, TC10and TC100 are linearly shown for the sake of convenience. However,actual track centers TC1, TC10 and TC100 are curved along thecircumferential direction of the disk 10. Thus, actual tracks TR1, TR10and TR100 are also curved along the circumferential direction of thedisk 10.

In the example shown in FIG. 3, when track TR1 is written to the innercircumferential area IR by head 15I shown in FIG. 2, fringing (outerfringing) having width (outer fringing width) FIa may be generated onthe external side from track center TC1. Fringing (inner fringing)having width (inner fringing width) FIb may be generated on the internalside from track center TC1. In this case, outer fringing width FIa isgreater than inner fringing width FIb (FIa>FIb). Outer fringing widthFIa includes distance (outer track distance) WIa between track centerTC1 of track TR1 and outer end portion Ea1 of track TR1, and distance(outer fringing gap) GIa between outer end portion Ea1 of track TR1 andouter position EIa affected by fringing, in other words, end portion EIaof outer fringing. Inner fringing width FIb includes distance (innertrack distance) WIb between track center TC1 of track TR1 and inner endportion Eb1 of track TR1, and distance (inner fringing gap) GIb betweeninner end portion Eb1 of track TR1 and inner position EIb affected byfringing, in other words, end portion EIb of inner fringing. The sum ofouter track distance WIa and inner track distance WIb is equivalent totrack width W1. In the example shown in FIG. 3, outer track distance WIais the same as inner track distance WIb. Thus, outer fringing gap GIa isgreater than inner fringing gap GIb (GIa>GIb).

In the example shown in FIG. 3, when track TR10 is written to the middlecircumferential area MR by head 15M shown in FIG. 2, outer fringinghaving width FMa and inner fringing having width FMb may be generated.In this case, outer fringing width FMa is substantially or completelythe same as inner fringing width FMb (FMa ≈FMb or FMa=FMb). Outerfringing width FMa includes outer track distance WMa between trackcenter TC10 of track TR10 and outer end portion Ea10 of track TR10, andouter fringing gap GMa between outer end portion Ea10 of track TR10 andend portion EMa of outer fringing. Inner fringing width FMb includesinner track distance WMb between track center TC10 of track TR10 andinner end portion Eb10 of track TR10, and inner fringing gap GMb betweenouter end portion Eb10 of track TR10 and end portion EMb of outerfringing. The sum of outer track distance WMa and inner track distanceWMb is equivalent to track width W10. In the example shown in FIG. 3,outer track distance WMa is the same as inner track distance WMb. Thus,outer fringing gap GMa is substantially or completely the same as innerfringing gap GMb (GMa≈GMb or GMa=GMb).

In the example shown in FIG. 3, when track TR100 is written by head 15Oshown in FIG. 2, outer fringing having width FOa and inner fringinghaving width FOb may be generated. In this case, inner fringing widthFOb is greater than outer fringing width FOa (FOa<FOb). Outer fringingwidth FOa includes outer track distance WOa between track center TC100of track TR100 and outer end portion Ea100 of track TR100, and outerfringing gap GOa between outer end portion Ea100 of track TR100 and endportion EOa of outer fringing. Inner fringing width FOb includes innertrack distance WOb between track center TC100 of track TR100 and innerend portion Eb100 of track TR100, and inner fringing gap GOb betweeninner end portion Eb100 of track TR100 and end portion EOb of innerfringing. The sum of outer track distance WOa and inner track distanceWOb is equivalent to track width W100. In the example shown in FIG. 3,outer track distance WOa is the same as inner track distance WOb. Thus,inner fringing gap GOb is greater than outer fringing gap GOa (Goa<Gob).

The driver IC 20 controls the driving of the SPM 12 and the VCM 14 inaccordance with the control of the system controller 130 (specifically,a micro processing unit [MPU] 60 as described later).

The head amplifier IC (preamplifier) 30 comprises a read amplifier and awrite driver (not shown). The read amplifier amplifies a read signalread from the disk 10 and outputs the read signal to the systemcontroller 130 (specifically, a read/write [R/W] channel 40 as describedlater). The write driver outputs write current to the head 15 inaccordance with the write data output from the R/W channel 40. The headamplifier IC 30 is electrically connected to the head 15 and the R/Wchannel 40.

The volatile memory 70 is a semiconductor memory in which the storeddata is lost when power supply is stopped. For example, data necessaryfor the process of each unit of the magnetic disk device 1 is stored inthe volatile memory 70. The volatile memory 70 is, for example, adynamic random access memory (DRAM) or a synchronous dynamic randomaccess memory (SDRAM).

The buffer memory 80 is a semiconductor memory which temporarilyrecords, for example, data transferred between the magnetic disk device1 and the host 100. The buffer memory 80 may be integrally formed withthe volatile memory 70. The buffer memory 80 is, for example, a DRAM, astatic random access memory (SRAM), an SDRAM, a ferroelectric randomaccess memory (FeRAM) or a magnetoresistive random access memory (MRAM).

The nonvolatile memory 90 is a semiconductor memory which retains thestored data even when power supply is stopped. The nonvolatile memory 90is, for example, a NOR or NAND flash read only memory (FROM).

The system controller (controller) 130 is realized by, for example,using a large-scale integration (LSI) circuit called a System-on-a-Chip(SoC), in which a plurality of elements are integrated into a singlechip. The system controller 130 includes the read/write (R/W) channel40, a hard disk controller (HDC) 50 and the microprocessor (MPU) 60. Thesystem controller 130 is electrically connected to the driver IC 20, thehead amplifier IC 30, the volatile memory 70, the buffer memory 80, thenonvolatile memory 90 and the host 100.

The R/W channel 40 performs the signal process of read data and writedata. The R/W channel 40 comprises a circuit or function for measuringthe signal quality of read data. The R/W channel 40 is electricallyconnected to the head amplifier IC 30, the HDC 50 and the MPU 60.

The HDC 50 controls data transfer between the host 100 and the R/Wchannel 40 in accordance with an instruction from the MPU 60 describedlater. The HDC 50 is electrically connected to the R/W channel 40, theMPU 60, the volatile memory 70, the buffer memory 80, the nonvolatilememory 90 and the host 100.

The MPU 60 is a main controller which controls each unit of the magneticdisk device 1. The MPU 60 performs servo control for controlling the VCM14 through the driver IC 20 and determining the position of the head 15.The MPU 60 controls the operation for writing data to the disk 10, andselects the storage destination of the write data transmitted from thehost 100. The MPU 60 controls the operation for reading data from thedisk 10, and controls the process of the read data transmitted from thedisk 10 to the host 100. In the following description, write data andread data may be simply referred to as data. The MPU 60 is connected toeach unit of the magnetic disk device 1. For example, the MPU 60 iselectrically connected to the R/W channel 40 and the HDC 50.

The MPU 60 includes a setting unit 61, a management unit 63 and a writecontroller 65. The MPU 60 performs the processes of these units onfirmware.

The setting unit 61 sets the track pitch between the target track and atrack (adjacent track) adjacent to the target track in normal recording.For example, on the basis of the inner fringing width when an adjacenttrack (outer adjacent track) is written to a position away from thetarget track on the external side, the setting unit 61 sets the trackpitch between the target track and the outer adjacent track. Similarly,on the basis of the outer fringing width when an adjacent track (inneradjacent track) is written to a position away from the target track onthe internal side, the setting unit 61 sets the track pitch between thetarget track and the inner adjacent track. The setting unit 61 recordsthe set track pitches in, for example, the system area 10 b or thenonvolatile memory 90.

FIG. 4 is a pattern diagram shown for explaining an example of a methodfor setting a track pitch according to the embodiment. In FIG. 4, tracksTR(N+1), TR(N) and TR(N−1) are arranged in the radial direction. FIG. 4shows track center TC(N+1) of track TR(N+1), track center TC(N) of trackTR(N), and track center TC(N−1) of track TR(N−1). The track width oftrack TR(N) is equivalent to the sum of outer track distance WMa(N) andinner track distance WMb(N). Track TR(N+1) is written to a position awayfrom track TR(N) on the external side with a particular track pitch(outer track pitch). Track TR(N−1) is written to a position away fromtrack TR(N) on the internal side with a particular track pitch (innertrack pitch). Outer fringing width FMa1 indicates the distance betweentrack center TC(N+1) and the position affected by the fringing generatedon the external side of track TR(N+1) when track TR(N+1) is written.Inner fringing width FMb1 indicates the distance between track centerTC(N+1) and the position affected by the fringing generated on theinternal side of track TR(N+1) when track TR(N+1) is written. Outerfringing width FMa2 indicates the distance between track center TC(N)and the position affected by the fringing generated on the external sideof track TR(N) when track TR(N) is written. Inner fringing width FMb2indicates the distance between track center TC(N) and the positionaffected by the fringing generated on the internal side of track TR(N)when track TR(N) is written. Outer fringing width FMa3 indicates thedistance between track center TC(N−1) and the position affected by thefringing generated on the external side of track TR(N−1) when trackTR(N−1) is written. Inner fringing width FMb3 indicates the distancebetween track center TC(N−1) and the position affected by the fringinggenerated on the internal side of track TR(N−1) when track TR(N−1) iswritten.

For example, the setting unit 61 writes the target track TR(N) to aparticular position of the disk 10, reads the written target trackTR(N), and measures the error rate (initial error rate) of the targettrack TR(N). Subsequently, the setting unit 61 writes the outer adjacenttrack TR(N+1) with a particular track pitch (outer initial track pitch)P(N) in relative to the target track TR(N), reads the written targettrack TR(N) again, and measures the error rate of the target track TR(N)again. The setting unit 61 determines whether the error rate is lessthan a threshold (outer threshold), or greater than or equal to theouter threshold. When the setting unit 61 determines that the error rateis greater than or equal to the outer threshold, the setting unit 61changes the outer initial track pitch P(N) in to the next outer trackpitch. In other words, when the setting unit 61 determines that thetarget track TR(N) is affected by fringing at the time of writing theouter adjacent track TR(N+1), the setting unit 61 changes the outerinitial track pitch P(N) in to the next outer track pitch, for example,to the next outer track pitch less than the outer initial track pitchP(N) in. Alternatively, the setting unit 61 may change the outer initialtrack pitch P(N) in to the next outer track pitch greater than the outerinitial track pitch P(N) in. The setting unit 61 determines whether theerror rate is less than the outer threshold, or greater than or equal tothe outer threshold again. When the setting unit 61 determines that theerror rate is greater than or equal to the outer threshold, the settingunit 61 changes the current track pitch to the next outer track pitch,for example, to the next outer track pitch less than the current trackpitch. Alternatively, the setting unit 61 may change the current trackpitch to the next outer track pitch greater than the current trackpitch. Until the error rate falls below the outer threshold, the settingunit 61 repeats a process for changing the current outer track pitch tothe next track pitch, writing the outer adjacent track TR(N+1) to aposition away from the target track TR(N) with the current (changed)outer track pitch and measuring the error rate of the target trackTR(N). When the setting unit 61 determines that the error rate is lessthan the outer threshold, the setting unit 61 sets the current outertrack pitch to the outer track pitch between the target track TR(N) andthe outer adjacent track TR(N+1). In other words, when the setting unit61 determines that the target track TR(N) is not substantially affectedby fringing at the time of writing the outer adjacent track TR(N+1), thesetting unit 61 sets the current outer track pitch to the outer trackpitch between the target track TR(N) and the outer adjacent trackTR(N+1). The setting unit 61 records the set outer track pitch in, forexample, the system area 10 b or the nonvolatile memory 90.

Similarly, the setting unit 61 writes the target track TR(N) to aparticular position of the disk 10, reads the written target trackTR(N), and measures the initial error rate of the target track TR(N).Subsequently, the setting unit 61 writes the inner adjacent trackTR(N−1) with a particular track pitch (inner initial track pitch) P(N−1)in relative to the target track TR(N), reads the written target trackTR(N) again, and measures the error rate of the target track TR(N)again. The inner initial track pitch P(N−1) in is set to a distance suchthat the outer fringing of the inner adjacent track TR(N−1) does nothave an effect on the target track TR(N). The setting unit 61 determineswhether the error rate is less than a threshold (inner threshold), orgreater than or equal to the inner threshold. When the setting unit 61determines that the error rate is greater than or equal to the innerthreshold, the setting unit 61 changes the inner initial track pitchP(N−1) in to the next inner track pitch. In other words, when thesetting unit 61 determines that the target track TR(N) is affected byfringing at the time of writing the inner adjacent track TR(N−1), thesetting unit 61 changes the inner initial track pitch P(N−1) in to thenext inner track pitch, for example, to the next inner track pitch lessthan the inner initial track pitch P(N−1) in. Alternatively, the settingunit 61 may change the inner initial track pitch P(N−1) in to the nextinner track pitch greater than the inner initial track pitch P(N−1) in.The setting unit 61 determines whether the error rate is less than theinner threshold, or greater than or equal to the inner threshold again.When the setting unit 61 determines that the error rate is greater thanor equal to the inner threshold, the setting unit 61 changes the currenttrack pitch to the next inner track pitch, for example, to the nextinner track pitch less than the current track pitch. Alternatively, thesetting unit 61 may change the current track pitch to the next innertrack pitch greater than the current track pitch. Until the error ratefalls below the inner threshold, the setting unit 61 repeats a processfor changing the current inner track pitch to the next track pitch,writing the inner adjacent track TR(N−1) to a position away from thetarget track TR(N) with the current (changed) inner track pitch andmeasuring the error rate of the target track TR(N). When the settingunit 61 determines that the error rate is less than the inner threshold,the setting unit 61 sets the current inner track pitch to the innertrack pitch between the target track TR(N) and the inner adjacent trackTR(N−1). In other words, when the setting unit 61 determines that thetarget track TR(N) is not substantially affected by fringing at the timeof writing the inner adjacent track TR(N−1), the setting unit 61 setsthe current inner track pitch to the inner track pitch between thetarget track TR(N) and the inner adjacent track TR(N−1). The settingunit 61 records the set inner track pitch in, for example, the systemarea 10 b or the nonvolatile memory 90. The outer threshold and theinner threshold may be the same as each other or different from eachother.

The setting unit 61 applies the above process to the disk 10, forexample, to the tracks located in a particular area of the data area 10a, and sets the outer and inner track pitches of the tracks located inthe particular area. The setting unit 61 records the set outer and innertrack pitches of the tracks located in the particular area in, forexample, the system area 10 b or the nonvolatile memory 90. Theparticular area is, for example, the middle circumferential area. Thesetting unit 61 may apply the above process to all the tracks of thedata area 10 a and set the outer and inner track pitches of all thetracks.

The management unit 63 sets the normal recording area CR and theshingled magnetic recording area SR on the disk 10, for example, in thedata area 10 a, based on the outer and inner track pitches set in thesetting unit 61, and manages the set normal recording area CR andshingled magnetic recording area SR.

For example, the management unit 63 compares the outer track pitch of aparticular track of the data area 10 a with the inner track pitch, andcalculates the difference between the outer track pitch and the innertrack pitch. The management unit 63 determines whether the difference isless than or equal to a reference value which is the threshold of thedifference, or greater than the reference value. When the managementunit 63 determines that the difference is less than or equal to thereference value, the management unit 63 sets the area to which thetarget track is written in the normal recording area CR, records, forexample, in the system area 10 b or the nonvolatile memory 90, theinformation of the set area to which the target track is written in thenormal recording area CR, and manages the information of the set area towhich the target track is written in the normal recording area CR by atable. The information of the area to which the target track is writtenincludes, for example, the track number, and the numbers of somedivisional areas (zones) of the data area 10 a. In this case, themanagement unit 63 determines whether or not the difference is zero.When the management unit 63 determines that the difference is not zero,the management unit 63 sets the less of the outer and inner trackpitches as the track pitch between the target track and the adjacenttracks (the outer and inner adjacent tracks), and records the set trackpitch in, for example, the system area 10 b or the nonvolatile memory90. When the management unit 63 determines that the difference is zero,the management unit 63 sets one of the outer track pitch and the innertrack pitch to the track pitch between the target track and the adjacenttracks, and records the set track pitch in, for example, the system area10 b or the nonvolatile memory 90. When the management unit 63determines that the difference is greater than the reference value, themanagement unit 63 sets the area to which the target track is written inthe shingled magnetic recording area SR, and records, for example, inthe system area 10 b or the nonvolatile memory 90, the information ofthe set area to which the target rack is written in the shingledmagnetic recording area SR. The reference value may be either a fixedvalue or a variable. The reference value may be changed. A plurality ofreference values may be set. For example, the reference value may be setfor either each zone or each head.

The management unit 63 applies the above process to the disk 10, forexample, to the tracks located in a particular area of the data area 10a, and sets, in the normal recording area CR, some areas to which, ofthe tracks, some tracks whose difference between the outer track pitchand the inner track pitch is less than or equal to the reference valueare written, respectively. The management unit 63 records, for example,in the system area 10 b or the nonvolatile memory 90, the information ofthe set areas to which the tracks are written in the normal recordingarea CR, and manages the information of the set areas to which thetracks are written in the normal recording area CR by a table. Themanagement unit 63 sets the disk 10 other than the normal recording areaCR, for example, the data area 10 a, in the shingled magnetic recordingarea SR. The management unit 63 records, for example, in the system area10 b or the nonvolatile memory 90, the information of the set areas towhich the tracks are written in the shingled magnetic recording area SR.The management unit 63 may perform the above process to all the tracksof the data area 10 a and set, in the normal recording area CR, someareas to which, of all the tracks, some tracks whose difference betweenthe outer track pitch and the inner track pitch is less than or equal tothe reference value are written, respectively. The management unit 63may set a plurality of normal recording areas CR, set the normalrecording area CR for each head and set a particular zone of the dataarea 10 a in the normal recording area CR.

Now, this specification shows some examples of the table TB of therecording area CR with reference to FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG.9, FIG. 10, FIG. 11 and FIG. 12.

FIG. 5 to FIG. 12 show some examples of the table TB of the normalrecording area CR according to the embodiment. In the examples shown inFIG. 5 to FIG. 12, the table TB is recorded in the nonvolatile memory90. The table shown in FIG. 5 to FIG. 12 may be recorded in the systemarea 10 b of the disk 10 or other memories, etc.

FIG. 5 shows an example of the table TB when a particular area of thedisk 10 is set in the normal recording area CR. In FIG. 5, the starttrack number is the number of the area to which the initial track iswritten in the normal recording area CR. The end track number is thenumber of the area to which the last track is written in the normalrecording area CR. Thus, the normal recording area CR is the areabetween the track of the start track number and the track of the endtrack number.

In the example shown in FIG. 5, the management unit 63 records the areasfrom the 150000^(th) area to the 160000^(th) area as the normalrecording area CR in the table TB. The management unit 63 sets the areaof the data area 10 a other than the normal recording area CR as theshingled magnetic recording area SR.

FIG. 6 shows an example of the table TB when a plurality of normalrecording areas CR are set. In FIG. 6, the normal recording area numberindicates the number of each set normal recording area CR. In FIG. 6,the table TB shows the start track number and the end track number foreach normal recording area number.

In the example shown in FIG. 6, the management unit 63 comprises, forexample, a reference value for each area in a particular range set inthe data area 10 a. Thus, the management unit 63 sets the normalrecording area CR for each area. The management unit 63 records, in thetable TB, the areas from the 150000^(th) area to the 160000^(th) area asthe 0^(th) normal recording area CR, the areas from the 165000^(th) areato the 170000^(th) area as the first normal recording area CR, the areasfrom the 180000^(th) area to the 185000^(th) area as the second normalrecording area CR, and the areas from the FFFFFFth area to the GGGGGGtharea as the maxth normal recording area CR. The management unit 63 setsthe area of the data area 10 a other than the normal recording area CRas the shingled magnetic recording area SR.

FIG. 7 shows an example of the table TB when the normal recording areaCR is set for each different head 15. In FIG. 7, the head numberindicates the number for identifying each different head 15. In FIG. 7,the table TB shows the start cylinder (or start track) number and theend cylinder (or end track) number for each head number.

In the example shown in FIG. 7, the management unit 63 comprises areference value for each different head 15. Thus, the disk 10 to whichthe normal recording area CR is set by the management unit 63 differsdepending on the head 15. The management unit 63 records, in the tableTB, the areas from the 150000^(th) area to the 160000^(th) area as thenormal recording area CR of the 0^(th) head 15, the areas from the165000^(th) area to the 170000^(th) area as the normal recording area CRof the first head 15, the areas from the 180000^(th) area to the185000^(th) area as the normal recording area CR of the second head 15,and the areas from the 149000^(th) area to the 153000^(th) area as thenormal recording area CR of the maxth head 15. The management unit 63sets the area of the data area 10 a other than the normal recording areaCR as the shingled magnetic recording area SR.

FIG. 8 shows an example of the table TB when at least one normalrecording area CR is set for each different head 15.

In the example shown in FIG. 8, the management unit 63 comprises areference value for each area in a particular range set in the data area10 a of the disk 10 of each different head 15. Thus, the management unit63 sets at least one normal recording area CR for each different head15. The management unit 63 records, in the table TB, the areas from the150000^(th) area to the 160000^(th) area as the normal recording area CRof the 0^(th) head 15, the areas from the 155000^(th) area to the160000^(th) area as the normal recording area CR of the first head 15,the areas from the 170000^(th) area to the 175000^(th) area as thenormal recording area CR of the first head 15, the areas from the160000^(th) area to the 170000^(th) area as the normal recording area CRof the second head 15, and the areas from the 149000^(th) area to the153000^(th) area as the normal recording area CR of the maxth head 15.The management unit 63 sets the area of the data area 10 a other thanthe normal recording area CR as the shingled magnetic recording area SR.

FIG. 9 shows an example of the table TB when a zone is set in the normalrecording area CR.

For example, when the difference between the outer track pitch and theinner track pitch of a specific track of the target zone is less than orequal to a reference value, the management unit 63 sets the target zonein the normal recording area CR. For example, the management unit 63 maybe configured to set the target zone in the normal recording area CRwhen the mean value of the differences between the outer track pitchesand the inner track pitches of the tracks included in the target zone isless than or equal to a reference value. For example, the managementunit 63 may be configured to set the target zone in the normal recordingarea CR when the differences between the outer track pitches and theinner track pitches of all the tracks included in the target zone areless than or equal to a reference value. In the example shown in FIG. 9,the management unit 63 records the 21^(st) zone as the normal recordingarea CR in the table TB. The management unit 63 sets the area of thedata area 10 a other than the normal recording area CR as the shingledmagnetic recording area SR.

FIG. 10 shows an example of the table TB when a plurality of normalrecording areas CR are set. In the table TB shown in FIG. 10, the zonenumber is shown for each normal recording area number.

In the example shown in FIG. 10, the management unit 63 comprises thereference value of the difference between the outer track pitch and theinner track pitch for each zone. Thus, the management unit 63 sets thenormal recording area CR for each zone. The management unit 63 records,in the table TB, the 21^(st) zone as the 0^(th) normal recording areaCR, the 22^(nd) zone as the first normal recording area CR, the 23^(rd)zone as the second normal recording area CR, and the FF^(th) zone as themaxth normal recording area CR. The management unit 63 sets the area ofthe data area 10 a other than the normal recording area CR as theshingled magnetic recording area SR.

FIG. 11 shows an example of the table TB when the normal recording areaCR is set for each different head 15. In the table TB shown in FIG. 11,the zone number is shown for each head number.

In the example shown in FIG. 11, the management unit 63 comprises thereference value of the difference between the outer track pitch and theinner track pitch for each different head 15. Thus, the disk 10 to whichthe normal recording area CR is set by the management unit 63 differsdepending on the head 15. The management unit 63 records, in the tableTB, the 23^(rd) zone as the normal recording area CR of the 0^(th) head15, the 21^(st) zone as the normal recording area CR of the first head15, the 22^(nd) zone as the normal recording area CR of the second head15, and the 23^(rd) zone as the normal recording area CR of the maxthhead 15. The management unit 63 sets the area of the data area 10 aother than the normal recording area CR as the shingled magneticrecording area SR.

FIG. 12 shows an example of the table TB when at least one normalrecording area CR is set for each different head 15.

In the example shown in FIG. 12, the management unit 63 comprises thereference value of the difference between the outer track pitch and theinner track pitch for each zone of the disk 10 of each different head15. Thus, the management unit 63 sets at least one normal recording areaCR for each different head. The management unit 63 records, in the tableTB, the 21^(st) zone as the normal recording area CR of the 0^(th) head15, the 21^(st) zone as the normal recording area CR of the first head15, the 22^(nd) zone as the normal recording area CR of the first head15, the 23^(rd) zone as the normal recording area CR of the second head15, and the 22^(nd) zone as the normal recording area CR of the maxthhead 15. The management unit 63 sets the area of the data area 10 aother than the normal recording area CR as the shingled magneticrecording area SR.

The write controller 65 writes a track to the normal recording area CRof the disk 10 set by the management unit 63 with the track pitch set inthe management unit 63 by normal recording, and writes a track to theshingled magnetic recording area SR of the disk 10 set by the managementunit 63 by shingled magnetic recording.

FIG. 13 is a flowchart showing a method for setting the track pitchbetween the target track and an adjacent track according to theembodiment.

The system controller 130 writes the target track to a particularposition of the disk 10 (B1301), and measures the initial error rate ofthe target track (B1302). The system controller 130 writes the outeradjacent track with the current outer track pitch relative to the targettrack (B1303), and measures the error rate of the target track again(B1304). The system controller 130 determines whether the error rate isgreater than or equal to the outer threshold, or less than the outerthreshold (B1305). When the system controller 130 determines that theerror rate is greater than or equal to the outer threshold (NO inB1305), the system controller 130 changes the current outer track pitchto the next outer track pitch (B1306), and proceeds to the process ofB1301. For example, the system controller 130 changes the current outertrack pitch to the next outer track pitch obtained by subtracting afirst particular value from the current outer track pitch.Alternatively, for example, the system controller 130 may change thecurrent outer track pitch to the next track pitch obtained by adding thefirst particular value to the current outer track pitch. The firstparticular value may be either a fixed value or a variable. When thesystem controller 130 determines that the error rate is less than theouter threshold (YES in B1305), the system controller 130 sets thecurrent outer track pitch as the outer track pitch between the targettrack and the outer adjacent track (B1307).

The system controller 130 writes the target track to a particularposition of the disk 10 (B1308), and measures the initial error rate ofthe target track (B1309). The system controller 130 writes the inneradjacent track with the current inner track pitch relative to the targettrack (B1310), and measures the error rate of the target track again(B1311). The system controller 130 determines whether the error rate isgreater than or equal to the inner threshold, or less than the innerthreshold (B1312). When the system controller 130 determines that theerror rate is greater than or equal to the inner threshold (NO inB1312), the system controller 130 changes the current inner track pitchto the next inner track pitch (B1313), and proceeds to the process ofB1308. For example, the system controller 130 changes the current innertrack pitch to the next inner track pitch obtained by subtracting asecond particular value from the current inner track pitch.Alternatively, for example, the system controller 130 may change thecurrent inner track pitch to the next inner track pitch obtained byadding the second particular value to the current inner track pitch. Thesecond particular value may be the same as or different from the firstparticular value. The second particular value may be either a fixedvalue or a variable. When the system controller 130 determines that theerror rate is less than the inner threshold (YES in B1312), the systemcontroller 130 sets the current inner track pitch as the inner trackpitch between the target track and the inner adjacent track (B1314), andproceeds to A.

FIG. 14 is a flowchart showing a method for setting the normal recordingarea and the shingled magnetic recording area according to theembodiment.

Subsequent to A of FIG. 13, the system controller 130 compares the outertrack pitch with the inner track pitch (B1401), and calculates thedifference between the outer track pitch and the inner track pitch(B1402). The system controller 130 determines whether the difference isless than or equal to the reference value, or greater than a referencevalue (B1403). The reference value is the threshold of the difference,and is different from the thresholds (the outer threshold and the innerthreshold) shown in FIG. 13. When the system controller 130 determinesthat the difference is greater than the reference value (NO in B1403),the system controller 130 records, for example, in the system area 10 bor the nonvolatile memory 90, the area to which the target track iswritten as the shingled magnetic recording area SR (B1404), andterminates the process. The system controller 130 may record the zoneincluding the target track as the shingled magnetic recording area SRin, for example, the system area 10 b or the nonvolatile memory 90.

When the system controller 130 determines that the difference is lessthan or equal to the reference value (YES in B1403), the systemcontroller 130 records, for example, in the system area 10 b or thenonvolatile memory 90, the area to which the target track is written asthe normal recording area CR (B1405). The system controller 130 mayrecord, for example, in the system area 10 b or the nonvolatile memory90, the zone including the target track as the normal recording area CR.The system controller 130 determines whether or not the difference iszero (B1406). When the system controller 130 determines that thedifference is zero (YES in B1406), the system controller 130 sets theouter track pitch or the inner track pitch as the track pitch betweenthe target track and the outer and inner adjacent tracks (B1407), andterminates the process. When the system controller 130 determines thatthe difference is not zero (NO in B1406), the system controller 130 setsthe less of the outer and inner track pitches as the track pitch betweenthe target track and the outer and inner adjacent tracks (B1408), andterminates the process.

According to the present embodiment, the magnetic disk device 1 sets thetrack pitch between the target track and the outer adjacent track basedon fringing when the outer adjacent track of the target track iswritten, and sets the inner track pitch between the target track and theinner adjacent track based on fringing when the inner adjacent track ofthe target track is written. The magnetic disk device 1 compares theouter track pitch with the inner track pitch, and calculates thedifference between the outer track pitch and the inner track pitch. Themagnetic disk device 1 determines whether the difference is less than orequal to a reference value, or greater than the reference value. Whenthe difference is less than or equal to the reference value, themagnetic disk device 1 records, for example, in the system area 10 b orthe nonvolatile memory 90, the area to which the target track is writtenas the normal recording area CR. When the outer track pitch is differentfrom the inner track pitch, the magnetic disk device 1 sets the less ofthe outer and inner track pitches as the track pitch between the targettrack and the outer and inner tracks. When the difference is greaterthan the difference, the magnetic disk device 1 records, for example, inthe system area 10 b or the nonvolatile memory 90, the area to which thetarget track is written as the shingled magnetic recording area SR.Thus, it is possible to provide a magnetic disk device capable ofeffectively writing data.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic disk device comprising: a disk; a headwhich writes data to the disk; and a controller which sets an area towhich a first track is written, based on a difference between a firsttrack pitch between the first track and the second track, which is setbased on fringing when writing a second track remote from the firsttrack of the disk in a first direction of a radial direction of thedisk, and a second track pitch between the first track and the thirdtrack, which is set based on fringing when writing a third track remotefrom the first track in a second direction opposite to the firstdirection.
 2. The magnetic disk device of claim 1, wherein thecontroller sets the area to which the first track is written, based on arelationship in size of the difference to a reference value.
 3. Themagnetic disk device of claim 1, wherein the controller sets the area towhich the first track is written to a shingled recording area if thedifference is greater than the reference value, and sets the area towhich the first track is written to a non-shingled recording area if thedifference is smaller than or equal to the reference value.
 4. Themagnetic disk device of claim 1, wherein the controller sets the firsttrack pitch, based on a first error rate corresponding to the secondtrack, and sets the second track pitch, based on a second error ratecorresponding to the third track.
 5. The magnetic disk device of claim4, wherein the controller makes the first track pitch greater if thefirst error rate is greater than a first threshold value, and makes thesecond track pitch greater if the second error rate is greater than asecond threshold value.
 6. A method for setting a recording area,applied to a magnetic disk device comprising a disk and a head whichwrites data to the disk, the method comprising: setting an area to whicha first track is written, based on a difference between a first trackpitch between the first track and the second track, which is set basedon fringing when writing a second track remote from the first track ofthe disk in a first direction of a radial direction of the disk, and asecond track pitch between the first track and the third track, which isset based on fringing when writing a third track remote from the firsttrack in a second direction opposite to the first direction.
 7. Themethod of claim 6, further comprising: setting the area to which thefirst track is written, based on a relationship in size of thedifference to a reference value.
 8. The method of claim 6, furthercomprising: setting the area to which the first track is written to ashingled recording area if the difference is greater than the referencevalue, and setting the area to which the first track is written to anon-shingled recording area if the difference is smaller than or equalto the reference value.
 9. The method of claim 6, further comprising:setting the first track pitch, based on a first error rate correspondingto the second track, and setting the second track pitch, based on asecond error rate corresponding to the third track.
 10. The method ofclaim 9, further comprising: making the first track pitch greater if thefirst error rate is greater than a first threshold value, and making thesecond track pitch greater if the second error rate is greater than asecond threshold value.
 11. A magnetic disk device comprising: a diskincluding a first area and a second area to which data is written in amanner different from the first area; a head which writes data to thedisk; and a controller which sets writing the first track to the firstarea or writing the second track based on a first track pitch between afirst track and a second track adjacent to an inner side of the firsttrack and a second track pitch between the first track and a third trackadjacent to an outer side of the first track.